Abstract

The phylogenetic relationships of the scleractinian genus Psammocora with the other genera
traditionally included in the family Siderastreidae and some Fungiidae are assessed based on
combined skeletal and molecular data. P. explanulata differs from the other examined
congeneric species (P. contigua, P. digitata, P. nierstraszi, P. profundacella, P.
superficialis, and P. stellata) in possessing interstomatous septa between adult corallites,
costae, and in having continuous buttress-like structures joining septal faces (i.e.,
fulturae) which typically occur in fungiids. These characters are shared with
Coscinaraea wellsi but not with the remainder of the examined siderastreids (the congeneric
C. columna, and Anomastraea irregularis, Horastrea indica, Pseudosiderastrea tayamai,
Siderastrea savignyana) whose septa are interconnected by typical synapticulae. Most of the
examined species form septa with distinct transverse groups of centers of calcification, a
biomineralization pattern typical of the Robusta clade. The observations on skeletal
structures corroborate the results of the ITS2 and 5.8S molecular phylogeny. C.wellsi and P.
explanulata are phylogenetically very close to each other and show closer genetic affinity
with the examined Fungiidae (Halomitra pileus, Herpolitha limax, Fungia paumotensis, and
Podabacia crustacea) than with the other species in the genera Psammocora and Coscinaraea,
or with any other siderastreid. Our results show that neither Psammocora nor Coscinaraea are
monophyletic genera. The high genetic distances between the species of Siderastreidae,
especially between Pseudosiderastrea tayamai and Siderastrea savignyana on one side and the
other genera on the other, suggest a deep divergence in the phylogenetic structure of the
family.